The Hypothesis of a Calendar Reform of 1194 AD -1195 AD
Hassig maintains that Aztec historical chronicles and annals, among them CodexAubin, suggest that the calendar date of the New Fire Ceremony may have been moved from 1 Rabbit (Ce Tochtli) to 2 Reed (Ome Acatl) in the years 1194 AD - 1195 AD, simply because these documents state that the rite was observed on the date 2 Reed (Ome Acatl). The evidence for this is that the date 2 Reed (Ome Acatl), corresponding to 1195 AD, is accompanied by a New Fire sign indicating that a shift of dates of celebrating the New Fire Ceremony had already occurred. But a calendar reform between 1194 AD - 1195 AD is never explicitly stated in these historical documents (Hassig 2001: 40; note 54, 176).
The Hypothesis of a Calendar Reform of 1246 AD -1247 AD
Folio 27v of Codex Telleriano-Remensis, which was painted in a Pre-European style, depicts the sign for the fire drill of the New Fire Ceremony beneath a Ome Acatl (2 Reed) sign (1247 ad) (fig. 12). But the fire drill sign is attached to the Ce Tochtli (1 Rabbit) sign of the year 1246 AD (Quinones Keber 1995: fol. 27v, 58; 208; Hassig 2001:114). 1246 AD - 1247 AD was the time of the long Aztec migration from Aztlan to Tenochtitlan. Three place names, Coatepetl, Tecontepetl and Piazcontepetl, are depicted on folio 27v (Quinones Keber 1995: fol. 27v, 58; 208; 271). Does this illustration symbolise a calendar reform of the New Fire Ceremony from Ce Tochtli (1 Rabbit) to Ome Acatl (2 Reed) between the years 1246 AD and 1247 AD?